1. 코드 분석

1. tlpi-dist/pmsg/pmsg_create.c

1. 코드

/* pmsg_create.c

   Create a POSIX message queue.

   Usage as shown in usageError().

   Linux supports POSIX message queues since kernel 2.6.6.
*/
#include <mqueue.h>
#include <sys/stat.h>
#include <fcntl.h>
#include "tlpi_hdr.h"

static void
usageError(const char *progName)
{
    fprintf(stderr, "Usage: %s [-cx] [-m maxmsg] [-s msgsize] mq-name "
            "[octal-perms]\n", progName);
    fprintf(stderr, "    -c          Create queue (O_CREAT)\n");
    fprintf(stderr, "    -m maxmsg   Set maximum # of messages\n");
    fprintf(stderr, "    -s msgsize  Set maximum message size\n");
    fprintf(stderr, "    -x          Create exclusively (O_EXCL)\n");
    exit(EXIT_FAILURE);
}

int
main(int argc, char *argv[])
{
    int flags, opt;
    mode_t perms;
    mqd_t mqd;
    struct mq_attr attr, *attrp;

    /* If 'attrp' is NULL, mq_open() uses default attributes. If an
       option specifying a message queue attribute is supplied on the
       command line, we save the attribute in 'attr' and set 'attrp'
       pointing to 'attr'. We assign some (arbitrary) default values
       to the fields of 'attr' in case the user specifies the value
       for one of the queue attributes, but not the other. */

    attrp = NULL;
    attr.mq_maxmsg = 10;
    attr.mq_msgsize = 2048;
    flags = O_RDWR;

    /* Parse command-line options */

    while ((opt = getopt(argc, argv, "cm:s:x")) != -1) {
        switch (opt) {
        case 'c':
            flags |= O_CREAT;
            break;

        case 'm':
            attr.mq_maxmsg = atoi(optarg);
            attrp = &attr;
            break;

        case 's':
            attr.mq_msgsize = atoi(optarg);
            attrp = &attr;
            break;

        case 'x':
            flags |= O_EXCL;
            break;

        default:
            usageError(argv[0]);
        }
    }

    if (optind >= argc)
        usageError(argv[0]);

    perms = (argc <= optind + 1) ? (S_IRUSR | S_IWUSR) :
                getInt(argv[optind + 1], GN_BASE_8, "octal-perms");

    mqd = mq_open(argv[optind], flags, perms, attrp);
    if (mqd == (mqd_t) -1)
        errExit("mq_open");

    exit(EXIT_SUCCESS);
}

2. 동작 모습

3. 디버깅 및 분석

• 메시지 큐 생성

2. tlpi-dist/pmsg/pmsg_send.c

1. 코드

/* pmsg_send.c

   Usage as shown in usageError().

   Send a message (specified as a command line argument) to a
   POSIX message queue.

   See also pmsg_receive.c.

   Linux supports POSIX message queues since kernel 2.6.6.
*/
#include <mqueue.h>
#include <fcntl.h>              /* For definition of O_NONBLOCK */
#include "tlpi_hdr.h"

static void
usageError(const char *progName)
{
    fprintf(stderr, "Usage: %s [-n] mq-name msg [prio]\n", progName);
    fprintf(stderr, "    -n           Use O_NONBLOCK flag\n");
    exit(EXIT_FAILURE);
}

int
main(int argc, char *argv[])
{
    int flags, opt;
    mqd_t mqd;
    unsigned int prio;

    flags = O_WRONLY;
    while ((opt = getopt(argc, argv, "n")) != -1) {
        switch (opt) {
        case 'n':   flags |= O_NONBLOCK;        break;
        default:    usageError(argv[0]);
        }
    }

    if (optind + 1 >= argc)
        usageError(argv[0]);

    mqd = mq_open(argv[optind], flags);
    if (mqd == (mqd_t) -1)
        errExit("mq_open");

    prio = (argc > optind + 2) ? atoi(argv[optind + 2]) : 0;

    if (mq_send(mqd, argv[optind + 1], strlen(argv[optind + 1]), prio) == -1)
        errExit("mq_send");
    exit(EXIT_SUCCESS);
}

2. 동작 모습

3. 디버깅 및 분석

3. tlpi-dist/pmsg/pmsg_receive.c

1. 코드

/* pmsg_receive.c

   Usage as shown in usageError().

   Receive a message from a POSIX message queue, and write it on
   standard output.

   See also pmsg_send.c.

   Linux supports POSIX message queues since kernel 2.6.6.
*/
#include <mqueue.h>
#include <fcntl.h>              /* For definition of O_NONBLOCK */
#include "tlpi_hdr.h"

static void
usageError(const char *progName)
{
    fprintf(stderr, "Usage: %s [-n] mq-name\n", progName);
    fprintf(stderr, "    -n           Use O_NONBLOCK flag\n");
    exit(EXIT_FAILURE);
}

int
main(int argc, char *argv[])
{
    int flags, opt;
    mqd_t mqd;
    unsigned int prio;
    void *buffer;
    struct mq_attr attr;
    ssize_t numRead;

    flags = O_RDONLY;
    while ((opt = getopt(argc, argv, "n")) != -1) {
        switch (opt) {
        case 'n':   flags |= O_NONBLOCK;        break;
        default:    usageError(argv[0]);
        }
    }

    if (optind >= argc)
        usageError(argv[0]);

    mqd = mq_open(argv[optind], flags);
    if (mqd == (mqd_t) -1)
        errExit("mq_open");

    /* We need to know the 'mq_msgsize' attribute of the queue in
       order to determine the size of the buffer for mq_receive() */

    if (mq_getattr(mqd, &attr) == -1)
        errExit("mq_getattr");

    buffer = malloc(attr.mq_msgsize);
    if (buffer == NULL)
        errExit("malloc");

    numRead = mq_receive(mqd, buffer, attr.mq_msgsize, &prio);
    if (numRead == -1)
        errExit("mq_receive");

    printf("Read %ld bytes; priority = %u\n", (long) numRead, prio);
    if (write(STDOUT_FILENO, buffer, numRead) == -1)
        errExit("write");
    write(STDOUT_FILENO, "\n", 1);

    exit(EXIT_SUCCESS);
}

2. 동작 모습

3. 디버깅 및 분석